Purification of olefins



June 20, 1967 R. D. RHODES, JR 3,326,999

' PURIFICATION- oF OLEFINS z E Di 2 [1 .1- E v f INVENTOR.

R. D. RHODES, JR.

w m Y ATTORNEYS United States Patent 3,326,999 PURIFICATION OF OLEFINS Ralph D. Rhodes, Jr., Pasadena, Tex., assignor to Phillips Petroleum Company, a corporation of Delaware Filed Aug. 1, 1963, Ser. No. 299,224 7 Claims. (Cl. 260-677) This invention relates to a method and apparatus for purifying a normally gaseous olefin stream. In another aspect it relates to efficient removal of entrained oil and other catalyst poisons from an olefin stream to be charged to a polymerization zone.

It has become accepted practice in the petrochemical industry to employ underground storage caverns for the storage of products, such as ethylene for which the requirements fluctuate, the cavern serving as a huge surge vessel. It is common that an olefin production reactor effluent be purified, compressed, and pumped into a mine salt formation cavern for storage, under pressure ranging up to 1100 p.s.i.g. The olefin being withdrawn is optionally passed thru a mist molecular sieve bed for removal of any solid or liquid contaminants that might have accidentally entered the system before passing to a pressure step-down means, wherein the stream pressure is reduced to between 500 and 600 p.s.i.g. The revolution in pressure is performed after the sieve.

Despite all of the foregoing purification steps, it was found that the olefin still contained significant amounts of catalyst poisons. It was found that stream dryers, such as bauxite desiccants could be used to purify the olefin sufiiciently, to reduce poisoning of catalyst, or preclude repeated catalyst poisoning and intolerable reactor shutdowns to replace or regenerate the catalyst. The bauxite dryers then, in time, become fouled with contaminants causing loss of capacity, and their frequent desiccant regeneration.

A heater is customarily employed downstream of the first pressure let-down means to overcome any tendency toward partial stream liquefaction due to the refrigeration effect of greatly reduced pressure. 7 While operating as described above it was observed that oil appeared at a leak around the stem of a valve positioned downstream of the heater. This oil very likely came from the lubrication oil used in the compressors for compressing the ethylene before it was passed into the storage caverns. The observation of leaking oil around the stem of the valve indicated that oil might be in such a state that it could be removed from the ethylene downstream of the heater. It was concluded that oil might be the principal material causing a deleterious effect on catalyst activity.

I then discovered that a mist eliminator located downstream of the heater would remove oil and any other poisons from the ethylene. The mist eliminator will effectively remove the oil and poisons, if a combination of pressure and temperature of said olefin stream is maintained such that the stream density is maintained below a predetermined value; and secondly, the stream is heated sufficiently high to meet the above predetermined density requirement, but notso high so that the stream temperature will not permit condensation of oil vapors upon passing to the coalescer. To meet this requirement in regard to entrained oils, the temperature should be in the range of 90 to 400 F. In the case of ethylene, the density must be below 5.2. lbs. per cubic foot.

By the practice of this invention, the bauxite-loaded dryers upstream of the reaction zone can be completely dispensed with, as the catalyst poisons are being inexpensively and successfully substantially removed with the novelly located eliminator, which is being operated under the critical conditions of stream density disclosed herein. The novel purification system has been installed in an 3,326,999 Patented June 20, 1967 "ice ethylene polymerization plant for several months without process shut down attributable to catalyst poisoning.

Among the normally gaseous olefins to which the present invention may be applied are ethylene, propylene, and =butenes. All of these are produced in large tonnages and require large storage capacities to even out differences between production and consumption. They further require high purity to be suitable for use in such sensitive reactions as polymerization.

Referring now to the drawing, in regard to which the invention will be described in further detail, as to a preferred embodiment, a stream of ethylene from a purification step (not shown) is passed via conduit 1 to a compressor 2, wherein the ethylene pressure is raised to about 1100 p.s.i.g. The compressed ethylene is passed to storage over brine via conduit 3 in underground storage 4. Ethylene, as required, is withdrawn via conduit 5 from cavern 3, is directed through a molecular sieve bed 5a, and passes to a first pressure control station, comprising pressure indicator controller 7 and motorized pressure let-down valve 8. The stream of ethylene enters the pressure let-down zone typically at 850 to 1050 p.s.i.g., F. and ethylene density ranging from 10 to 18 lb./ft. The stream 9 exits valve 8, typically at 600 p.s.i.g., 40 F.

The refrigeration effect, described by Joule-Thompson, which occurs when substantially reducing the pressure on a high pressure normally gaseous stream, is frequently strong enough to cause partial liquefaction of the stream. In order to overcome this refrigeration effect for purposes of accurate fiow measurements, and achieving the desired stream density, a heater 11 is preferably disposed in stream -9. It may conveniently be of the shell and tube type. The heated ethylene 12 exits heater 11, typically at 600 p.s.i.g., 100 F., and density about 3.8 lb./ft. The density change attributable to this heating step is deemed significant in the subsequent effective removal of oil.

The oil separation means 13 of this invention is positioned in stream 12 for effective removal of entrained oil and catalyst poisons from the ethylene. A suitable oil coalescer for this purpose is the V. D. Anderson Mist Extractor Type L, --a division of the International Basic Economy Corp., Cleveland 2, Ohio. Accumulated oil is drained frequently from coalescer 13 Via valved drain line 14.

The substantially oiland contaminants-free ethylene stream 16 passes thru a second pressure control station, comprising PIC 17 and motorized pressure let-down valve 18. Stream 19 exits valve 18 typically at 500 p.s.i.g., F., and density of about 3.2 lb./ft This ethylene stream is now suitable for passage to one or more polymerization reactor trains feed conduits 21a, b, or c, and the now substantially contaminants-free ethylene (or other olefin) stream passes directly to the polymerization zones as illustrated.

It will be necessary to determine the stream density which is critical to the operation of the invention. To operate according to the present invention it is necessary that the stream temperature and pressure are such that the stream density does not exceed 5.2 lbs. per cubic foot. Further, the temperature must be maintained above the saturation temperature of the olefin from which the oil is being separated, but not above 400 F.

-Reasona'ble variation, modification, and alteration of the invention will become apparent from a study of the disclosure, the drawing, and the appended claims to those 7 skilled in the art.

which permits the operation of subsequently described step (c);

(c) passing the processed olefin stream thru an oil separation means -for substantially complete removal of entrained contaminants; and

(d) passing the now substantially contaminants-free olefin stream directly to said reaction zone.

2. A method of purifying a normally gaseous ethylene stream of entrained oil and other catalyst poisons comprising:

(a) passing a high pressure ethylene stream to be purified thru a pressure reduction means to bring the stream pressure down to a level suitable for charging to a reaction zone;

- (b) heating the reduced pressure ethylene stream to bring the stream temperature to a level suitable for charging to said polymerization zone; the resulting combination of pressure and temperature of said ethylene stream being such that the ethylene density is below 5.2 lbs./ft ,-Which permits the operation of subsequently described step (c); and (c)passing the processed ethylene stream'thru an oil separation means for substantially complete removal of entrained contaminants. p 3. A method of purifying anormally gaseous ethylene stream of entrained on and other catalyst poisons comprising: Y

(a) passing a high pressureethylene stream to be purified thru a pressure reduction means to bring the stream-pressure down to a level suitable for charging to a reaction zone; i

e (b) heating the reduced pressure ethylene stream to bring the stream temperature to 'a level suitable for charging to said polymerization zone; the resulting combination of pressure and temperature of said ethylene stream being such that the ethylene density is'below 5.2 lbs./ft ,fwhich permits the operation-of subsequently described step (c);

(c) passing the processed ethylene stream thru an oil separation means for substantially complete removal 'of'en'trained contaminants; and

(d) passing the now substantially contaminants-free ethylene stream directly to said reaction zone.

4. -A method of purifying a normally gaseous ethylene stream of entrained oil and other catalyst poisons comprising:

(-a) raising a high-pressuree-thylene stream to be puri fied thru a pressure reduction means to bring the stream pressuredown'to' a level in the range of 600 m to 300 p.s.i.g. suitable for charging to a polymeriza- (b) heating the reduced" pressure ethylene stream to :bring the stream't'emperature to a level suitable for charging to said polymerization zone; the resulting combination of pressure and temperature of said ethylene stream beingsuch that the ethylene density is'below5l2 lbs/ft. which permits theoperation of I subsequently described step (c') i (c) passing the processed ethylene stream thru an oil separation means for substantially complete removal of entrained contaminants; and

(d) passing thenow substantially contaminants-free I ethylene stream directly to said polymerization zone.

5. A method of purifying 'a normally. gaseous ethylene stream v of entrained oil and other catalyst poisons comprising:

(a) passing a high pressure ethylene stream to :be purified thru a pressure reduction means to bring the stream pressure down to a level suitable for charging to a polymerization zone;

(b) heating the reduced pressure ethylene stream to bring the stream temperature to a level in the range of F. to 400 F. suitable for charging to said polymerization zone; the resulting combination of pressure and temperature of said ethylene stream being such that the ethylene density is below about 4.5 lbs/ft. which permits the operation of subsequently described step (c);

(c) passing the processed ethylene stream thru an oil separation means for substantially complete removal of entrained contaminants; and

(d) passing the now substantially contaminants-free ethylene stream directly to said polymerization zone.

6. A method of purifying a normally gaseous ethylene stream of entrained oil and other catalyst poisons comprising:

(a) passing a high pressure ethylene stream to be purified from a storage source thru a pressure reduction means to bring the stream pressure down to a level in the range of 600 to 300 p.s.i.g. suitable for charging to a polymerization zone;

(b) heating the reduced pressure ethylene stream to bring the stream temperature to a level in the range of 90 F. to 400 'F. suitable for charging to said polymerization zone; the resulting combination of pressure and temperature of said ethylene stream being such that the ethylene density is below about 4.5 lbs/ft. which permits the operation of subsequently described step (c);

(c) passing the processed ethylene stream thru an oil separation means for substantially complete removal of entrained contaminants; and

(d) passing the now substantially contaminants-free ethylene stream directly to said polymerization zone.

7. A method of purifying a normally gaseous ethylene stream of entrained oil and other catalyst poisons comprising:

(a) compressing a purified ethylene to high pressure;

(b) storing said compressed ethylene in an underground storage cavern under high pressure;

(c) passing a high pressure ethylene stream to be purified from a storage source thru a pressure reduction means to bring the stream pressure down to a level in the range of 600 to 300 p.s.i.g. suitable for charging to a polymerization zone;

((1) heating the reduced pressure ethylene stream to bring the stream temperature to a level in the range of 90 F. to 400 F. suitable for charging to said polymerization zone; the resulting combination of pressure and temperature of said ethylene stream being such that the ethylene density is below about 4.5 lbs/ft. which permits the operation of subsequently described step (e);

(e)' passing the processed ethylene stream thru an oil separation means for substantially complete removal of entrained contaminants; and

(f) passing the now substantially contaminants-free ethylene stream directly to said polymerization zone.

References Cited DELBERT E. GANTZ, Primary Examiner.

' ALPHONSO D. SULLIVAN, Examiner. 

1. A METHOD OF PURIFYING A NORMALLY GASEOUS OLEFIN STREAM OF ENTRAINED OIL AND OTHER CATALYST POISONS COMPRISING: (A) PASSING A HIGH PRESSURE OLEFIN STREAM TO BE PURIFIED THRU A PRESSURE REDUCTION MEANS TO BRING THE STEAM PRESSURE DOWN TO A LEVAL SUITABLE FOR CHARGING TO A REACTION ZONE; (B) HEATING THE REDUCED PRESSURE OLEFIN STREAM, AS REQUIRED TO BRING THE STREAM TEMPERATURE TO A LEVEL SUITABLE FOR CHARGING TO SAID ZONE; THE RESULTING COMBINATION OF PRESSURE AND TEMPERATURE OF SAID OLEFIN STREAM BEING SUCH THAT THE OLEFIN DENSITY IS BELOW 5.2 LBS./FT.3 AND SAID OLEFIN IS IN THE VAPOR PHASE, WHICH PERMITS THE OPERATION OF SUBSEQUENTLY DESCRIBED STEP (C); 